1. Field of the Invention
The present invention relates to a magnetic head employing a magnetoresistive device, and more particularly to a technique for providing a magnetic head that has a reduced amount of change in asymmetry with respect to the MR height, and that exhibits better reproduction characteristics
2. Description of the Related Art
In magnetic heads for use in VCRs, data storage units of computers, etc., the track width has been narrowed in recent years as a result of an increase in recording density and conversion into a digital form of signal recording.
Against such a background, various MIG (Metal In Gap) magnetic heads have hitherto been employed. An MIG magnetic head has a structure with a pair of magnetic core halves, each of which is fabricated by forming, on a core half made of ferrite or ceramic, a metal magnetic thin film having superior soft magnetic characteristics. The core halves are joined to each other by a bonding material, such as a fusing glass, with an insulating film interposed between the magnetic core halves.
Recently, in an attempt to obtain narrower tracks than those possible in MIG magnetic heads, efforts have been made to apply a magnetic head utilizing a magnetoresistive device (MR device) as a device for reproducing magnetic recording information in VCRs, data storage units, etc.
FIG. 13 shows the sectional structure of a principal part of a conventional magnetic head. This magnetic head comprises two half cores, an MR head section for reproduction, and a write head section for recording, both of the head sections being formed between the half cores.
As shown in FIG. 13, an MR head section 110 for reproduction is formed on an insulating layer 104 that is formed on an end surface 103a of one half core 103. The MR head section 110 is made up of a lower shield layer 112 and a lower insulating layer 113, which are successively formed on the insulating layer 104 in that order, a magnetoresistive device (hereinafter referred to as an xe2x80x9cMR devicexe2x80x9d) 120 is formed on the lower insulating layer 113 and is exposed to a medium sliding surface 102. An upper insulating layer 114 covers the MR device 120, and an upper shield layer 115 is formed on the upper insulating layer 114. The upper shield layer 115 also serves as a lower core layer for a write head section 111 described below.
The write head section 111 is made up of a lower core layer (upper shield layer) 115, a gap layer 116 and a coil 117, which are successively formed on the lower core layer 115 in that order, an upper insulating layer 118 covering the coil 117, and an upper core layer 119 joined at one end to the gap layer 116 and at the other end to the lower core layer 115 on the side of the coil 117.
More specifically, a base end 119b of the upper core layer 119 is magnetically coupled to the lower core layer 115 in a substantially central portion of the coil 117. A core protective layer 130 made of, e.g., alumina, is formed on the upper core layer 119, and the other half core (not shown) is joined to the core protective layer 130 from above.
The MR device 120 is formed of a thin film of a soft magnetic alloy such as a Nixe2x80x94Fe alloy, and is connected to an MR electrode 121. The MR device 120 is also exposed at its part to the medium sliding surface 102, and has the MR height h of a predetermined dimension in a direction perpendicular to the medium sliding surface 102 (i.e., in a direction of arrow Z shown in FIG. 13).
As will be described later, the dimension of the MR height h of the MR device 120 gives an important effect upon reproduction characteristics of the MR head section 110, and therefore the dimensional accuracy of the MR height h must be closely managed. Usually, the MR height h is adjusted by polishing the medium sliding surface 102.
A Nixe2x80x94Fe alloy film has hitherto been used in the MR device 120, and it is known that the magnitude of a reproduction output from the MR head section 110 depends upon the magnetostriction constant of the Nixe2x80x94Fe alloy film. In a conventional magnetic head, therefore, a Nixe2x80x94Fe alloy film with the magnetostriction constant having a positive value is used to increase the reproduction output. In order to make positive the magnetostriction constant of the Nixe2x80x94Fe alloy film, the composition ratio of Fe must not be lower than 19% by weight.
For the above-mentioned reason, most of MR devices used in conventional magnetic heads are formed of Nixe2x80x94Fe alloys in which the composition ratio of Fe is not lower than 19% by weight.
On the other hand, in the case of employing a digital magnetic recording method, the symmetry in peak heights of a reproduction signal obtained by a magnetic head, i.e., the so-called asymmetry, occurs as a problem to be considered in addition to the magnitude of the reproduction output. The reproduction signal in a digital magnetic recording shows a waveform defined by a series of successive pulse waveforms that are reversed alternately in the positive and negative directions. If the symmetry in peak heights of successive pulse waveforms reversed alternately in the positive and negative directions is deteriorated, read errors may be increased.
Preventing the occurrence of read errors requires a reproduction signal having good symmetry, that is, by reducing the asymmetry of a magnetic head to 0%. The asymmetry of a magnetic head depends upon the MR height h of the MR device 120.
Although the MR height h is adjusted by polishing the medium sliding surface 102, the polishing accuracy is about 0.01 xcexcm at a minimum and hence a variation in asymmetry may sometimes occur.
To suppress the variation in asymmetry, it is therefore necessary that the change in asymmetry be kept as small as possible, even with a change in the MR height h on the order of 0.01 xcexcm.
Although a conventional magnetic head employing the MR device 120 whose magnetostriction constant has a positive value is superior in the reproduction output, it is disadvantageous in providing a larger amount of change in asymmetry with respect to the MR height h. An improvement in polishing accuracy of the MR height h should be effective in suppressing a variation in asymmetry. In the present state of the art, however, it is difficult to further improve the polishing accuracy of the MR height. Thus, the variation in asymmetry of the magnetic head cannot be suppressed to a satisfactory level.
Additionally, with an increase in magnetic recording density, an increased reproduction rate is demanded, and the use of higher frequencies to produce a recording magnetic field is likewise demanded. Precise reading of a recording magnetic field at higher frequencies requires a magnetic head having a higher resolution. However, the resolution of a conventional magnetic head is not sufficient for satisfying the above demand.
The inventors have made intensive studies with a view to overcoming the problems described above, and have found that there is a specific relationship between the asymmetry of a magnetic head and the magnetostriction constant of an MR device. Based on such a specific relationship, the inventors have accomplished the present invention.
In view of the state of the art described above, it is an object of the present invention to provide a magnetic head that has a smaller amount of change in asymmetry (i.e., symmetry in peak heights of a reproduction signal) with respect to the MR height, and has an improved resolution for the reproduction signal.
To achieve the above object, the present invention is constituted as follows.
According to one aspect of the present invention, there is provided a magnetic head including a magnetoresistive device as a read device for reading magnetic recording information recorded on a magnetic recording medium while contacting the magnetic recording medium, wherein a magnetostriction constant of a soft magnetic substance forming the magnetoresistive device is 0 or below.
With the magnetic head having the above feature, since the magnetostriction constant of the magnetoresistive device (hereinafter referred to as the xe2x80x9cMR devicexe2x80x9d) is 0 or below, the amount of change in asymmetry (i.e., symmetry in peak heights of a reproduction signal) with respect to the MR height is significantly reduced. Therefore, even when the MR height is slightly changed, the asymmetry does not vary significantly.
In the aforementioned magnetic head, the magnetostriction constant of the soft magnetic substance forming the MR device is preferably in a range of not less than xe2x88x923xc3x9710xe2x88x926 and not more than 0.
When the magnetostriction constant of the MR device is not less than xe2x88x923xc3x9710xe2x88x926, the reproduction output of the magnetic head is prevented from lowering excessively. When the magnetostriction constant of the MR device is not more than 0, the amount of change in asymmetry with respect to the MR height is reduced, and the asymmetry does not vary significantly, even with a slight change in the MR height.
In the aforementioned magnetic head, the soft magnetic substance forming the MR device is preferably a Nixe2x80x94Fe alloy, and the composition ratio of Fe in the Nixe2x80x94Fe alloy is in a range of not smaller than 17.5% by weight, but not larger than 18.8% by weight.
In the magnetic head having the above features, by employing a Nixe2x80x94Fe alloy having the Fe composition ratio of not smaller than 17.5% by weight, but not larger than 18.8% by weight, as the soft magnetic substance forming the MR device, the magnetostriction constant of the MR device can be maintained in the range of not less than xe2x88x923xc3x9710xe2x88x926 and not more than 0. As a result, the reproduction output of the magnetic head is prevented from lowering excessively, and the asymmetry does not vary significantly, even with a slight change in the MR height.
In the aforementioned magnetic head, the magnetostriction constant of the soft magnetic substance forming the MR device is preferably in a range of not less than xe2x88x923xc3x9710xe2x88x926 and not more than xe2x88x920.5xc3x9710xe2x88x926.
When the magnetostriction constant of the MR device is not less than xe2x88x923xc3x9710xe2x88x926, the reproduction output of the magnetic head is prevented from lowering excessively. When the magnetostriction constant of the MR device is not more than xe2x88x920.5xc3x9710xe2x88x926, the resolution in detecting a recording signal on the magnetic recording medium is improved so as to be adaptable for a higher frequency of the recording signal.
In the aforementioned magnetic head, the soft magnetic substance forming the MR device is preferably a Nixe2x80x94Fe alloy, and a composition ratio of Fe in the Nixe2x80x94Fe alloy is in a range of not smaller than 17.5% by weight and not larger than 18.5% by weight.
In the magnetic head having the above features, by employing a Nixe2x80x94Fe alloy having the Fe composition ratio of not smaller than 17.5% by weight and not larger than 18.5% by weight as the soft magnetic substance forming the MR device, the magnetostriction constant of the MR device can be maintained in the range of not less than xe2x88x923xc3x9710xe2x88x926 and not more than xe2x88x920.5xc3x9710xe2x88x926. As a result, the reproduction output of the magnetic head is prevented from lowering excessively, and the resolution in detecting a recording signal on the magnetic recording medium is improved so as to be adaptable for a higher frequency of a reproduction signal. According to another aspect of the present invention, there is provided a magnetic head including two or more magnetoresistive (MR) devices as read devices for reading magnetic recording information recorded on a magnetic recording medium while contacting the magnetic recording medium, wherein a magnetostriction constant of a soft magnetic substance forming each of the magnetoresistive devices is 0 or below.
In the magnetic head having the above features, the magnetostriction constant of each MR device is 0 or below, and the amount of change in asymmetry (i.e., symmetry in peak heights of a reproduction waveform) with respect to the MR height is thereby reduced. Therefore, even when a slight variation in the MR height occurs among the MR devices, the asymmetry does not vary significantly in the entire magnetic head.
In the aforementioned magnetic head, the magnetostriction constant of the soft magnetic substance forming each MR device is preferably in a range of not less than xe2x88x923xc3x9710xe2x88x926 and not more than 0.
In the aforementioned magnetic head, the magnetostriction constant of the soft magnetic substance forming each MR device is preferably in a range of not less than xe2x88x923xc3x9710xe2x88x926 and not more than xe2x88x920.5xc3x9710xe2x88x926.
Furthermore, in a magnetic head having a plurality of MR devices, the rate of acceptable final products manufactured is given by multiplying the rates of acceptable respective MR devices by one another. Accordingly, the rate of acceptable final products tends to be reduced to a large extent as the number of MR devices per head increases. By employing the above construction, however, the rate of acceptable final products can be remarkably improved when manufacturing a magnetic head including a plurality of MR devices.